The present invention relates broadly to a signal processing apparatus, and in particular to a recursive signal processing apparatus.
In many prior art data transmission schemes the information resides in the position of a signal pulse within some fixed range of positions. This range may be defined by the transmission of an independent synch pulse as in certain telemetry systems, by the generation of the transmitted pulse as in radar and sonar, or by any other means whereby the zero position to which the signal pulse is referenced is made known to the receiver. Each such transmission we refer to as a scan. In this general context there have arisen several fairly conventional methods of signal enhancement. These methods may be divided into three categories.
The first category is simple scan-to-scan non-coherent integration which may be performed easily, causing the signal to be enhanced to a degree depending largely upon the rate at which the signal position changes between consecutive scans. The more constant the signal position, the longer can be made the time constant of the integration. The fact that the signal position changes slowly, or in a continuous manner, from scan to scan is not explicitly taken advantage of.
The second category is the large variety of tracking schemes which originated in sonar and radar applications. These schemes may properly be regarded as signal enhancement techniques that depend upon exploiting the local linear nature of the signal path. More complex schemes which employ quadratic extrapolation, are merely a continuation of the same idea. These techniques typicaly differ from those disclosed here in the following respects.
The logic of these procedures is complicated, consisting usually of two distinct modes: the acquisition and the tracking modes. Some computation must normaly be devoted to processing the video such as thresholding, and scan-to-scan integration. The computational burden in each mode is high, and in tracking mode, each signal must be extrapolated, and logic devised to determine when the track must be considered lost. Additional logic in the acquisition mode must keep account of transitory tracks, and decide when acquisition is to be confirmed. The difficulties created by the possible crossing of tracks must be resolved. Thus, careful signal bookkeeping is an important part of the effort. Normally, the enhancement of the signal is purely binary: i.e. when it has been assigned a track, a signal is wholly enhanced; if not the signal is effectively invisible.
The third category comprises procedures based purely upon thresholded data: i.e., the intensity of each scan is prethresholded, so that the raw data consists solely of pulses, some of which may be noise, and, typically, at most one of which is signal. The usual procedures to achieve signal enhancement in this setting consist essentially of favoring that pulse which has been computed to belong to the strongest local linear trend. The linearity is not critical in such procedures (e.g. quadratic trends could be examined), but the fact that continuity is being examined locally makes the restriction to straight lines reasonable as well as computationally convenient.